... a rare two-headed golden-crowned kinglet!
Of course, the bird had one head; I was trying to take photos with insufficient light and this is how my digital camera tried to solve the problem. Multiple exposures have been around since photography was invented; it was a widely-used technique for producing fraudulent "ghost" photos.
Here's a somewhat better photo:
A small flock of these lovely little birds were busy in my front garden (they especially liked the seeds of the garlic chives), but by the time I remembered to get out there with a camera, it was twilight. I keep hoping they'll show up again in better light, but while I'm waiting, here's the photos I got.